Nickel electrodeposition process and auxiliary nickel anode alloy



United States Patent 3,449,224 NICKEL ELECTRODEPOSITION PROCESS AND AUXILIARY NICKEL ANODE ALLOY George A. Di Bari, Haverstraw, and Clarence H. Sample, St. James, N.Y., and Burton B. Knapp, Allendale, N.J., assignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 17, 1966, Ser. No. 586,979 Int. Cl. C23b 5/08; B01k 3/06 U.S. Cl. 204-49 8 Claims The present invention is directed to the electrodeposition of nickel and, more particularly, to an improved soluble nickel material particularly useful as an auxiliary anode in nickel plating, which material is characterized by substantial freedom from the production of sludge which can create roughness in a nickel deposit when the material is employed as a nickel plating anode without an anode bag.

Consumable nickel anodes are normally employed in the electrodeposition of nickel and may be classified according to function as primary anodes or as auxiliary anodes. The chief function of primary nickel anodes is to dissolve anodically and thereby replace the nickel being removed by electrodeposition.

In modern high production nickel plating, for example, in the electroplating of automotive bumpers and other complex parts, a continuing problem has been that of providing as uniform a coating of electrodeposited nickel as possible while avoiding either excessive buildup of nickel on more accessible areas on the work being plated and avoiding the production of undesirably thin nickel deposits on less accessible portions of the work being plated. It will be understood that many large shapes, for example, automotive bumpers, are complex in design and the problem of providing a nickel coating of substantially uniform thickness over the area thereof, including both protuberant and recessed areas, is difficult. In order to achieve maximum economy in the use of nickel while at the same time providing over the entire surface of the work being plated at least the minimum quantity of nickel required for a particular service, the auxiliary anode plating practice has become recognized as a particularly advantageous solution to the vexing problem. In carrying out the auxiliary anode practice, each part to be plated is carefully studied and a rack to hold the part during the plating operation is specially constructed when a suflicient run of similar parts is being made to justify the cost. It is often necessary to fasten the auxiliary anode required for plating a particular part to the same rack as the work being plated. Provisions are made .to insulate the anode from the work (which is connected :as cathode in the bath) and to supply current thereto. When this practice is employed, the auxiliary anode accompanies the work throughout the entire plating cycle in which a number of different baths are employed for cleaning, plating, etc. Almost all parts which receive a nickel coating are thereafter chromium plated and when an auxiliary anode is employed it usually accompanies the work in the chromium plating bath as well as in the nickel plating bath. In addition, it is frequently found that a plurality of different nickel plating baths, e.g., a semi-bright bath and a bright bath, is employed. A copper plating bath may also be included in the plating cycle. For this reason, anode bags cannot be used on auxiliary anodes since plating solution or other solution trapped within the bags would contaminate the following bath in the plating cycle. Accordingly, the auxiliary anode must be capable of use without anode bags. The auxiliary anode can be an insoluble or nonconsum-able anode, for example, a platinized titanium anode can be used without an anode bag. However, nonconsumable anodes create plating bath ice problems in connection with pH control, metal depletion and chlorine evolution. Accordingly, the auxiliary anode is preferably a consumable, i.e., soluble, anode.

Nickel in various forms, for example, electrolytic nickel, wrought nickel and cast nickel, is employed as the primary anode material in plating. 'However, these common forms of nickel almost invariably require the use of anode bags to prevent escape from the vicinity of the anode of any metallic or nonme-tallic particles which are generated anodically during corrosion of the material. Accordingly, the common nickel anode materials presently available are not capable of use as unbagged auxiliary anodes since metallic and nonmetallic particles generated during the corrosion thereof will become included in the nickel deposit with resulting roughness and unsatisfactory appearance of the deposit. it is not economical under present day conditions to remove such roughness by mechanical treatment of the plated articles as by bulling or the like. In addition, as previously noted, the plating cycle may be so constructed that once the work to be plated is mounted in the plating rack, it is not removed therefrom until the completion of the plating operation.

We have now discovered a new Wrought nickel auxiliary anode material which can be employed without anode bags and which dissolves uniformly without the production of roughness-producing particles.

It is :an object of the present invention to provide an improved wrought nickel anode material which may be employed as an auxiliary anode without the production of roughness-producing particles.

Other objects and advantages of the invention will become apparent from the following description.

Generally speaking, the present invention is directed to a wrought nickel material especially useful as an unb'agged auxiliary anode in nickel plating which contains, by weight, about 1% to 3% silicon, about 0.1% to about 0.35% carbon, with the silicon content being at least about 3.4 or 4 times the carbon content, not more than about 0.015% sulfur, up to about 0.1% magnesium, with the magnesium content being at least 2.5 times the sulfur content, up to about 0.1% copper, and the balance essentially nickel. In producing the special auxiliary anode material, the silicon content is maintained at a level of at least about 1% and the carbon content is maintained at a level of at least about 0.1% in order that the material will corrode actively as anode in common nickel plating baths without the production of roughness-producing particles such as metallic nickel flakes, etc. However, the silicon content does not exceed about 3% to minimize or prevent the formation of excessive quantities of nonmetallic residues during corrosion of the unbagged auxiliary anode and the carbon content does not exceed about 0.35% because it then becomes diflicult to prevent the formation of graphitic carbon in the auxiliary anode material. Graphitic carbon can produce roughness of the cathode deposit during corrosion of an unbagged auxiliary anode made of soluble nickel if present therein. More advantageously, carbon is controlled in the range of about 0.2% to about 0.35% and silicon in the range of about 1% to about 1.5%, respectively, to insure the presence of an activating amount of carbon, e.g., at least about 0.1% carbon, in surface layers at least after a deskinning operation to remove about 0.01 inch of the anode surface as described hereinafter when surface decarburization occurs during processing, e.g., mill heating and hot-rolling, etc., and to minimize production of nonmetallic residue during anodic dissolution. The ratio of silicon to carbon is maintained at about 3.4 or 4 or higher to insure smooth dissolution of the anode and prevent release therefrom of roughness-producing particles when the anode is used without a bag. In ususal melting practice, a small amount of sulfur is unavoidably included in the nickel material. However, the sulfur content should be controlled so as not to exceed about 0.015% and, more preferably, so as not to exceed about 0.01% since excessive sulfur contents can create roughness-producing particles. Magnesium is employed in the melting of the material in an amount at least 2.5 times the sulfur present and usually in an amount not exceeding about 10 times the sulfur present in order to prevent sulfur embrittlement of the nickel material and to prevent the production of roughness-producing particles due to the sulfur content when the anode is corroded. Magnesium does not exceed about 0.08% or about 0.1% since excessive magnesium can itself contribute to the production of roughness-producing particles. Copper in small amounts not exceeding about 0.1% may be present in the anode material without harmful effects. The remainder of the composition is essentially nickel.

The auxiliary anode material may be employed without anode bags in usual nickel plating baths, including bright nickel plating baths, the Watts bath, the all-chloride bath, the sulfamate bath, etc. Such baths contain at least about 3 grams per liter (g.p.l.) of chloride ions and, more advantageously, at least about 10 g.p.l. of chloride ions. Satisfactory nickel plating bath compositions contain up to about 400 g.p.l., e.g., about 25 to about 330 g.p.l., of nickel sulfate (NiSO -6H O), about 3 to about 350 g.p.l., e.g., about 10 to about 300 g.p.l., of nickel chloride (NiCl -6H O), up to about 7 g.p.l. of nickel sulfamate, up to about 300 g.p.l. of nickel fiuoborate, and about 25 to about 40 g.p.l. of boric acid. The nickel ion concentration in these baths is about 50 to about 150 g.p.l., the baths are operated in the pH range of about 1.5 to about 5, at cathode current densities of up to about 300 or 400 amperes per square foot (a.s.f.), and at temperatures from room temperature up to about 160 F. Any of the usual proprietary chloride-containing semibright and bright nickel plating baths and any of the usual proprietary chromium plating baths may be employed. The special anode material corrodes actively and smoothly in such nickel plating baths at anode current densities over the range of about to about 100 a.s.f. without the production of roughness-producing particles at the cathode and without the use of anode bags.

In order to give those skilled in the art a better understanding and/ or a better appreciation of the advantages of the invention, the following illustrative examples are given:

EXAMPLE I Nickel materials having compositions as set forth in the following Table I were produced by air melting and casting to ingots which were then heated to about 2100 F. and hot rolled to rods about 1% inches in diameter.

TABLE I Anode No. Percent Si Percent 0 Percent S Percent Mg Percent Cu The hot rolled, oxidized surface was removed from the rods. The materials were employed as anode without bags in a test cell provided with a bath containing 300 grams per liter of nickel sulfate (NiSO -6H O), 45 grams per liter of nickel chloride (NiCl -6H O) and about 40 grams per liter of boric acid. The bath pH was about 4 and was operated at a temperature of 125 F. The anode was placed horizontally in the bath at the center of a U-shaped cathode placed therearound such that the parallel arms of the U were also horizontal and the cathode was about one inch from the anode face. The horizontal face or shelf of the U beneath the cathode had an area of about 2 square inches. The current was passed from the anode to a TABLE II Anode No: Roughness rating Experience has indicated that an anode providing a roughness rating less than 5 in the foregoing test behaves well in production whereas materials with a rating between 5 and 10 show marginal behavior and materials with a rating above 10 give results which are not acceptable in production.

EXAMPLE II A commercial scale melt containing about 0.27% carbon, about 1.26% silicon, about 0.01% sulfur, about 0.03% copper, about 0.033% magnesium, and the balance nickel, was produced as an air melted ingot. The ingot was soaked at about 2100 F. and was reduced to a bar about 1% inches in diameter by hot rolling. A portion of the bar was treated by electrochemical pickling in a solution containing equivalent amounts of hydrochloric acid and water using an anode current density of about a.s.f. so as to remove about 10 mils of material from the surface thereof. When subjected to the test described in Example I, a roughness rating of 1.7 was obtained.

Since the nickel material is heated to temperatures on the order of 2000 F. to about 2200 F. in a furnace atmosphere during the heating prior to hot rolling and is subjected to the atmosphere at elevated temperatures during and after completion of the hot rolling operation, it is found that some decarburization of the surface layer upon the nickel material is encountered. The dccarburized surface can become depleted in carbon and can contain rolled-in oxide as a result of the heating and hot rolling operations. Since this surface layer does not have the required composition to achieve the effects sought in accordance with the invention, it is removed by conventional means such as mechanical abrasion, grinding, machining, electrochemical pickling, etc. These surface treatment operations remove the mill scale and the decarburized zone and expose the basis metal having the specially controlled composition contemplated in accordance with the invention to the action of the nickel electroplating bath in use. Electrochemical pickling or deskinning is the preferred treatment for reasons of economy. A satisfactory deskinning treatment comprises immersion of the anode material, e.g., as a rod, in a hydrochloric acid solution containing, for example, equal volumes of concentrated hydrochloric acid and water and passing current through the material at an anodic current density of about 50 to 100 a.s.f. to remove mill scale, embedded oxide, etc. from the surface. Removal of surface material from the hot rolled product to a depth of about 10 mils is generally sufficient.

The alloy is malleable and may readily be converted to wrought form from the ingot stage by conventional hot working. To minimize precipitation of graphitic carbon, the material desirably is quenched after hot working.

While the special material provided in accordance with the invention is particularly applicable to auxiliary anode service in nickel plating, it may also be employed as a primary anode material, particularly in instances where the ability to perform without anode bags is desired.

We claim:

1. In the electrodeposition of nickel wherein soluble primary nickel anodes are immersed in the bath to supply the principal nickel requirements for plating and soluble nickel auxiliary anodes, are employed to improve the current distribution to work being plated so as to secure a more uniform distribution of electrodeposited nickel upon the work being plated than is the case when such auxiliary anodes are not employed, the improvement which comprises employing as said auxiliary anode a wrought nickel material containing about 1% to about 3% silicon, about 0.1% to about 0.35% carbon, with the silicon content being at least about 3.4 times the carbon content, not more than about 0.015% sulfur, up to about 0.1% magnesium, with the magnesium content being at least about 2.5 times the sulfur content, up to about 0.1% copper and the balance essentially nickel, said auxiliary anode being characterized by substantial freedom from sludge production when used without a bag.

2. The process according to claim 1 wherein the auxiliary anode material contains about 0.2% to about 0.35% carbon.

3. The process according to claim 2 wherein the auxiliary anode material contains about 1% to about 1.5% silicon.

4. The process according to claim 1 wherein the auxiliary anode material contains about 1% to about 1.5% silicon.

5. An improved nickel anode capable of being supplied in wrought form and particularly useful as an unbagged auxiliary anode in nickel plating and containing about 1% to about 3% silicon, about 0.1% to about 0.35% carbon, with the silicon content being .at least about 3.4 times the carbon content, not more than about 0.015 sulfur, up to about 0.1% magnesium, with the magnesium content being at least about 2.5 times the sulfur content, up to about 0.1% copper and the balance essentially nickel.

6. The anode material according to claim 5 wherein the carbon content is about 0.2% to about 0.35%.

7. The anode material according to claim 6 wherein the silicon content is about 1% to about 1.5

8. The anode material according to claim 5 wherein the silicon content is about 1% to about 1.5

References Cited UNITED STATES PATENTS 2,117,284 5/1938 Bieber et al. 204293 XR 2,304,059 12/1942 Bieber et al. 204-293 XR 2,504,239 4/1950 Rochl 204-293 XR HOWARD S. WILLIAMS, Primary Examiner.

G. L. KAPLAN, Assistant Examiner.

US. Cl. X.R. 170; 204-293 

1. IN THE ELECTRODEPOSITION OF NICKEL WHEREIN SOLUBLE PRIMARY NICKEL ANODES ARE IMMERSED IN THE BATH TO SUPPLY THE PRINCIPAL NICKEL REQUIREMENTS FOR PLATING AND SOLUBLE NICKEL AUXLIARY ANODES ARE EMPLOYED TO IMPROVE THE CURRENT DISTRIBUTION TO WORK BEING PLATED SO AS TO SECURE A MORE UNIFORM DISTRIBUTION OF ELECTRODEPOSITED NICKEL UPON THE WORK BEING PLATED THAN IS THE CASE WHEN SUCH AUXILIARY ANODES ARE NOT EMPLOYED, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS SAID AUXILIARY ANODE A WROUGHT NICKEL MATERIAL CONTAINING ABOUT 1% TO ABOUT 3% SILICON, ABOUT 0.1% TO ABOUT 0.35% CARBON, WITH THE SILICON CONTENT BEING AT LEAST ABOUT 3.4 TIMES THE CARBON CONTENT, NOT MORE THAN ABOUT 0.015% SULFUR, UP TO ABOUT 0.1% MAGNESIUM, WITH THE MAGNESIUM CONTENT BEING AT LEAST ABOUT 2.5 TIMES THE SULFUR CONTENT, UP TO ABOUT 0.1% COPPER AND THE BALANCE ESSENTIALLY NICKEL, SAID AUXILIARY ANODE BEING CHARACTERIZED BY SUBSTANTIAL FREEDOM FROM SLUDGE PRODUCTION WHEN USED WITHOUT A BAG.
 5. AN IMPROVED NICKEL ANODE CAPABLE OF BEING SUPPLIED IN WROUGHT FORM AND PARTICULARY USEFUL AS AN UNBAGGED AUXILIARY ANODE IN NICKEL PLATING AND CONTAINING ABOUT 1% TO ABOUT 3% SILICON, ABOUT 0.1% TO ABOUT 0.35% CARBON, WITH THE SILICON CONTENT BEING AT LEAST ABOUT 3.4 TIMES THE CARBON CONTENT, NOT MORE THAN ABOUT 0.015% SULFUR, UP TO ABOUT 0.1% MAGNESIUM, WITH THE MAGNESIUM CONTENT BEING AT LEAST ABOUT 2.5 TIMES THE SULFUR CONTENT UP TO ABOUT 0.1% COPPER AND THE BALANCE ESSENTIALLY NICKEL. 